1. Field of the Invention
The present invention relates to a Plasma Display Panel (PDP), and more particularly, to a PDP with multiple dielectric layers on a rear glass plate.
2. Description of the Related Art
A PDP, which is a device for displaying characters or graphics using light emitted from a plasma during a gas discharge, is an emissive flat display panel utilizing a gas discharge.
PDPs are categorized into a Direct Current (DC) PDP and an Alternating Current (AC) PDP according to the method of applying a drive voltage to the discharge cells. A DC PDP has electrodes directly exposed to a plasma and the discharge current directly flows through the electrodes, requiring separate external resistance for limiting the current. On the other hand, an AC PDP has electrodes covered by a dielectric layer, that is, the electrodes are not directly exposed to a plasma, thereby protecting the electrodes from ionic impact during discharge. Also, the AC PDP is advantageous in that a displacement current flows through the electrodes. The AC PDP can be classified according to the electrode structure of a discharge cell into an opposite discharge PDP, a surface discharge PDP, and a partition discharge PDP. In particular, the surface discharge PDP is advantageous in that electrode portions where a discharge occurs are arranged on one substrate and phosphor layers are arranged on the other substrate so that deterioration of the phosphor layers due to ion bombardment during a discharge is suppressed.
An AC surface discharge PDP includes a front substrate and a back substrate. The front substrate has a plurality of sustain electrodes and a plurality of scanning electrodes arranged thereon, and a bus electrode is disposed on each of the plurality of sustain electrodes and the plurality of scanning electrodes. A front dielectric layer is formed to cover the electrodes arranged on the front substrate, and a protective layer formed of MgO is formed to cover the front dielectric layer. The back substrate has a plurality of address electrodes arranged thereon. The plurality of sustain electrodes and scanning electrodes arranged on the front substrate, and the plurality of address electrode arranged on the back substrate, intersect, i.e., they are orthogonal to each other, the front substrate and the back substrate being parallel to each other. A back dielectric layer is formed on the back substrate to cover the plurality of address electrodes. A plurality of partitions are arranged on the back dielectric layer and red, green and blue phosphors are coated between each of the plurality of partitions.
The AC surface discharge PDP is driven using charges on the dielectric layer covering the electrodes, that is, wall charges. An address discharge is caused at a discharge space formed between each of the plurality of sustain electrodes and scanning electrodes arranged on the front substrate and each of the plurality of address electrodes arranged on the back substrate so as to be opposite to and face the sustain electrodes and scanning electrodes, thereby achieving a surface discharge. AC surface discharge PDPs that are currently being produced have a luminance of approximately 350cd/m2 and an output efficiency of approximately lm/W. Theoretically, a high luminance of greater than 500 cd/m2 and a high output efficiency of greater than 4 lm/W can be achieved by a gas discharge performed by a PDP. In reality, however, a peak luminance of a Cathode Ray Tube (CRT) is approximately 700 cd/m2 and the efficiency thereof is not greater than several lm/W. Thus, it is necessary to further improve a luminance and efficiency of a PDP.
Various techniques for producing PDPs having improved luminance have been proposed. Particularly, a technique of increasing reflectivity has been used. In other words, when a gas discharge occurs at a discharge cell of a PDP, visible light is generated so that phosphors are excited to emit the visible light. In order to cause as much as visible light to travel toward a front portion of the PDP, it is necessary to increase reflectivity. One way to increase reflectivity is by adding an additive, that is, a white pigment of a metal oxide, to a back dielectric layer, the white pigment being at least one selected from the group consisting of alumina (Al2O3), titanium oxide (TiO2), yttrium oxide (Y2O3), magnesium oxide (MgO), calcium oxide (CaO), tantalum oxide (Ta2O5), silicon oxide (SiO2), and barium oxide (BaO). This technique is disclosed in Japanese Laid-Open Patent Publication No. 1999-60272, and Japanese Patent Laid-Open Patent Publication No. 1998-74455.
Such attempts for increasing reflectivity by adding an additive to a back dielectric layer, however, still have limitations. That is, as the amount of the white pigment added to the back dielectric layer increases, the reflectivity of the back dielectric layer increases but results in a deterioration in the conductivity of the dielectric layer due to an increase in the dielectric constant of the dielectric layer. Thus, a withstanding voltage of the dielectric layer is reduced, ultimately leading to a breakdown when a discharge occurs at a discharge cell of the PDP.
Another way of increasing the reflectivity is forming a reflective layer on surfaces of partitions and the dielectric layer, as disclosed in Japanese Laid-Open Patent Publication No. 2000-11885. According to this technique, separately from the dielectric layer, a TiO2 layer is formed on the surface of the dielectric layer and the surface of the partitions. However, a withstanding voltage between cells is lowered, causing a breakdown during a discharge. Thus, in order to ensure an electrical insulating property, it is necessary to remove a reflective layer made of metal oxide formed on the partitions, which makes the process complicated, increasing the production cost of the PDP.